A new person of interest, the third sought in relation to the investigation, was seen near the Eagle Drive shops wearing black pants and a black hoodie shortly after Ms Blackwood's death.
He is described as about 177 centimetres tall, of medium build, with a muscular torso.
Witnesses saw him walking along The Avenue from the direction of the Eagle Drive shops, possibly carrying a brown paper bag.
"This is a separate person again," said homicide squad Detective Senior Sergeant David Snare.
"We'd like to speak to that person just in case he may be able to assist us with our inquiries. He may be a witness, he may have just been walking down the street and have no knowledge of it. But we need to find out who he is and speak to him."
Early inquiries into Ms Blackwood's death were hampered because two different men wearing striped tops were seen near the home on the day of the murder and police believed they were looking for one man.
The coincidence cost the investigation about two weeks, Sergeant Snare said.
